A radio frequency power amplifier used in a radio communications apparatus, such as a cellular phone, in a mobile communications system is classified roughly into a radio frequency power amplifier part that amplifies a radio frequency power and a bias control part that supplies the radio frequency power amplifier part with a direct current voltage. Further, usually, the power amplifier mounts these parts in a module substrate and is constituted as a radio frequency power amplifier module.
The bias control part controls an operating current and an operating voltage of the radio frequency power amplifier part so that the radio frequency power amplifier part can maintain a stable radio frequency characteristic against a change in the environment, such as a temperature change, and is very important. The radio frequency power amplifier part is usually controlled by changing a bias voltage at the input side of a semiconductor element that constitutes the radio frequency power amplifier part.
The bias voltage is supplied from the bias control part to the radio frequency power amplifier part via a bias supply line. At this occasion, if a radio frequency signal leaks to the bias control part through the bias supply line, the bias control part becomes unstable in an operation depending on the leakage signal. When the amount of leakage is increased, that results in an erroneous operation.
A series inductance is inserted into the bias supply line to suppress such an erroneous operation with a radio frequency signal. Consequently, the bias supply line reaches high impedance in the frequency of the radio frequency signal and the radio frequency signal arriving at the bias control part is attenuated. Conventionally, chip components or a spiral structure formed in a semiconductor element was used as this inductance.
Still more, there is an example that a bonding wire for wiring formed on a module substrate is used as an inductance. The example in which the inductance with such a bonding wire is used in a part of the wiring of a semiconductor amplifier element that is not for a bias supply line is disclosed in Japanese Patent Laid-Open No. H6(1994)-224660.